Substrate layer for dichroic photoconductors

ABSTRACT

In an electrophotographic plate suitable for use in dichroic contact reflex reproduction a novel substrate layer of polyamide is inserted between the dichroic sensitizer and the conductive base.

United States Patent [54] SUBSTRATE LAYER FOR DICl-IROIC PHOTOCONDUCTORS 7 Claims, No Drawings 96/].6, 96/88 51 int. c1 G03g 5/04 [50] Field of Search 96/1, 1.5, 1.6, 88; 252/501 56] References Cited UNITED STATES PATENTS 2,660,526 1 1/1953 Herrick 96/75 3,113,022 12/1963 Cassiers et a1. 96/15 3,317,317 5/1967 Clark .I: 96/1 Primary Examiner-George F. Lesmes Assistant Examiner-R. E. Martin Attorneys- Hanifin and Jancin and Joseph G. Walsh ABSTRACT: In an electrophotographic plate suitable for use in dichroic contact reflex reproduction a novel substrate layer of polyamide is inserted between the dichroic sensitizer and the conductive base.

SUBSTRATE LAYER FOR DICHROIC PHOTOCONDUCTORS FIELD OF THE INVENTION PRIOR ART The process for using dichroic photoconductors in contact reflex reproduction is described in detail in U.S. Pat. application Ser. No. 668,697, filed Sept. 18, 1967 by Herrick and Shattuck. In this process, a document is positioned adjacent a photoconductive element which exhibits photoconductive dichroism and has a preferred absorption axis, and in which the photoconductive element is uniformly exposed through the photoconductive element with polarized light whose vector, relative to the absorption axis, is such that the light is not absorbed. The polarized light in striking the document is absorbed in some areas, normally the dark image areas, and depolarized and reflected in others, normally the light background areas. The light from the reflected areas, being depolarized, contains light with an electric vector which will be absorbed by the photoconductive element and the element is thus exposed to a pattern corresponding to the pattern of the document. This renders the photoconductive element conductive and capable of transporting an electrostatic charge and, hence, permits the formation of an electrostatic charge pattern corresponding to the document.

The preferred type of plate for use in the above-described process contains (from top to bottom):

a. a charge transport layer, for example one made of polyvinylcarbazole,

b. a dichroic sensitizer, and

c. a semitransparent conductive base, for example cellulose triacetate with a metallized surface, or a thin polycarbonate film or NESA glass.

SUMMARY OF THE INVENTION According to the present invention, improved results are obtained when there is added to the above-described prior art plate a new layer, called a substrate layer. This layer separates the dichroic sensitizer and the semitransparent conductive base. It has now been discovered that improved performance is obtained when such a layer is inserted in the plate when, and only when, the layer is made of polyamide. In particular, the high humidity aging stability is vastly improved. The explanation for this unexpected result is not clearly understood.

There were many requirements which had to be met by a material before it could be used as the substrate layer in the present invention. Preferably it should give good adhesion to the conductive base and to the charge transport layer. At the same time, it must not be tacky, but should present a hard surface so that the dichroic sensitizer can be oriented on it. It should not absorb visible light, and should not be soluble in organic solvents such as benzene, chloroform, toluene, or tetrahydrofuran. In addition, it should be sufficiently conductive to allow electrophotographic decay without increasing residual potential. Numerous materials were tried and the only one found which satisfactorily met all the above requirements was polyamide.

It is preferred that the polyamide have a resistivity of less than l ohm cm. For optimum results the polyamide should have a resistivity of less than 10 ohm cm. The substrate polyamide layer preferably should be less than 2 microns in thickness, but, particularly with the polyamides having low resistivity, the thickness may be as great as about 5 microns.

As mentioned above, polyamides having low resistivity are preferred. The performance of a polyamide having a high resistivity may be improved by adding to it a small amount (from traces up to about 1 percent) of certain electron acceptor materials which act as sensitizers. These materials include, for example, alizarin yellow 06, p-chloronil, tetracyanoethylene, tetrabromophthalic anhydride, and the dyes listed in U.S. Pat. Nos. 3,037,861, 3,169,060 and 3,287,113.

PREFERRED EMBODIMENTS The general nature of the invention having been set forth, the following examples are now presented as to the specific preparation of preferred embodiments of the invention. The specific details presented are for purposes of illustration and not limitation.

EXAMPLE I A 5 percent solution of Emerez 3794 R (a thermoplastic polyamide resin from Emery Industries, Inc.) in n-propyl alcohol was coated on aluminized polycarbonate (optical density= 1.0) and cured at 100 C. for 15 minutes after air drying.

A dichroic sensitizer was oriented on the polyamide surface in a unilateral direction. The sensitizer was 2,6-bis(p-N,N- dimethylaminobenzylideneamino)-benzo[ l,2-d:4,5-d'] bisthiazole, which may be prepared as described in U.S. Pat. application Ser. No. 668,697, filed Sept. 18, 1967, now U.S. Pat. No. 3,598,982.

The following formulation was coated on the polyamide/dichroic layer to a thickness of about 7 microns.

Polyvinylcarbazole 5.0 g. (10 percent) in benzene 0.001 g. 2,4,7 trinitro-9 fluorenone Curing was for 5 minutes at 100 C.

The above coating was capable of sustaining an electrophotographic corona charge and decaying when exposed to light. Aging of this sample for 2 hours at 100 C. and percent relative humidity showed no degradation of electrophotographic properties.

EXAMPLE II A 4 percent solution of Elvamide 8061 (an alcohol soluble polyamide resin from DuPont) in methanol was coated on aluminized polycarbonate (optical density 1.0) and cured immediately to prevent clouding at 100 C.

The dichroic sensitizer compound from example I was oriented unilaterally on top the polyamide resin.

The following formulation was coated 10 1. thick over the polyamide.

55 g. 10% polyvinylcarbazole in benzene 5 g. Benzene 30 g. chloroform 10 g, Toluene 7 g. 1% Acryloid Al 1 in benzene 0.01 g. 2,4,7 trinitrofluorenone l dp. DC-ZOO-IOOO (Acryloid A-l 1 is an adhesive copolymer of esters of acrylic and metacrylic acid from Rohm and Haas. DC-200-1000 is a dimethyl siloxane lubricant from Dow Coming) The film was cured for one hour at C. and good image quality was obtained from the dichroic robot.

EXAMPLE III The process of example II was repeated, but Elvamide 8061 in ethanol instead of methanol was used. Good image quality was obtained.

EXAMPLE IV 4. An electrophotographic plate as claimed in claim I wherein the polyamide la microns.

yer has a thickness of less than 5 5. An electrophotographic plate as claimed in claim I wherein the polyamide la microns.

yer has a thickness of less than 2 6 An electrophotographic plate as claimed in claim 1 wherein the charge transport layer is polyvinylcarbazole.

7. An electrophotographic plate as claimed in claim I wherein the polyamide la sensitizer.

yer contains an electron acceptor 

2. An electrophotographic plate as claimed in claim 1 wherein the polyamide has a resistivity of less than 1014 ohm cm.
 3. An electrophotographic plate as claimed in claim 1 wherein the polyamide has a resistivity of less than 1010 ohm cm.
 4. An electrophotographic plate as claimed in claim 1 wherein the polyamide layer has a thickness of less than 5 microns.
 5. An electrophotographic plate as claimed in claim 1 wherein the polyamide layer has a thickness of less than 2 microns.
 6. An electrophotographic plate as claimed in claim 1 wherein the charge transport layer is polyvinylcarbazole.
 7. An electrophotographic plate as claimed in claim 1 wherein the polyamide layer contains an electron acceptor sensitizer. 